Method for concurrently producing at least a pair of semiconductor structures that each include at least one useful layer on a substrate

ABSTRACT

A method for concurrently producing at least a pair of semiconductor structures that each include at least one useful layer on a substrate. The method includes providing an initial structure that includes a useful layer having a front face on a support substrate. Atomic species are implanted into the useful layer to a controlled mean implantation depth to form a zone of weakness within the useful layer that defines first and second useful layers. Next, a stiffening substrate is bonded to the front face of the initial structure. The first useful layer is then detached from the second useful layer along the zone of weakness to obtain a pair of semiconductor structures with a first structure including the stiffening substrate and the first useful layer and a second structure including the support substrate and the second useful layer. The structures obtained can be used in the fields of electronics, optoelectronics or optics.

BACKGROUND ART

[0001] This invention generally relates to a method of concurrentlyproducing at least two structures, each having at least one useful layeron a substrate, for applications in the fields of electronics,optoelectronics or optics. In particular, the method includes providingan initial structure that includes a useful layer having a front face ona support substrate, implanting atomic species to form a zone ofweakness within the useful layer, bonding a stiffening substrate isbonded to a front face of the initial structure, and detaching a firstuseful layer from a second useful layer along the zone of weakness toobtain a pair of semiconductor structures. The first structure includesthe stiffening substrate and the first useful layer and the secondstructure includes the support substrate and the second useful layer.

[0002] Several layer transfer methods are known. One concerns implantingatomic species under the surface of a source substrate to create a zoneof weakness which delimits a thin layer. The next step is to contact thefree face of this thin layer with a support substrate, then to detachthe thin layer from the remainder of the source substrate and totransfer it to the support substrate. A description of this type ofmethod can be found in the art with reference to the method known underthe registered trademark “SMART-CUT®”. Use of this method results ingenerating a source substrate remainder that can be recycled and reusedduring a future layer transfer. However, this process involves polishingand finishing operations that can be long and costly, due to both thecost of the materials used and the time spent on them. In addition, forsome extremely hard materials such as silicon carbide, theaforementioned recycling steps can prove to be very long and difficult.

[0003] Another known layer transfer method is called “Bond and Etch BackSilicon on Insulator” (“BESOI”). This technique involves a burning-inmethod and/or chemical etching treatment via chemical attack used aftermolecular bonding a source substrate to a support substrate. The freesurface (or rear face) of this source substrate is then polished until athin layer of desire thickness is obtained on the support. It is to benoted that such a method destroys the majority of the source substrateas each structure is made, so this technique is not economically viable,especially when the thin layer material is expensive.

[0004] Lastly, Silicon on Insulator (“SOI”) type materials include alayer of thick silicon covering a buried layer of silicon dioxide (SiO₂)and a transferred superficial layer of silicon, and the same problemsconcerning recycling exist for the silicon material used to form thetransferred layer. In addition to the aforementioned recycling problems,it is difficult to transfer very thin layers, meaning layers that areless than 100 nanometers (100 nm) thick when using the SMART-CUT® typemethod. Indeed, thin layers transferred in such manner have numerousdefects, such as blisters. The defects may be due to, for example,treatments used to strengthen the bonding interface between the thinlayer and the support substrate.

[0005] The problems concerning transferring very thin good qualitylayers also exist for SOI substrates. In particular, is noted that thetransferred layer of silicon if an SOI structure has defects when lessthan a certain thickness, for example 20 nm. The defects can increase ifa high temperature thermal treatment is also used. In this regard,reference can be made to the article by Q.-Y. Tong, G. Cha, R. Gafiteauand U. Gösele, “Low temperature wafer direct bonding”, J.Microelectomech Syst., 3, 29, (1994).

[0006] During thermal treatments, for example to strengthen the bondinginterface (which is known as “stabilizing”) after detachment occurs, agas is created in the bonding interface. In the case of a thick SOIsubstrate, the transferred layer is thick and fills the role of astiffener. In the case of a thin SOI substrate in which the transferredlayer and/or the oxide layer are thin, the aforementioned absorption andstiffening phenomena do not take place and sue of a gas leads to poorbonding.

[0007] In addition, as described in published International ApplicationNo. WO 01/115218, implantation of atomic species and detachment of thewafer create defects that are principally concentrated on the inside ofthe layer to be transferred. It has been observed that the thinner thelayer the poorer the quality that results.

SUMMARY OF THE INVENTION

[0008] A method for concurrently producing at least a pair ofsemiconductor structures that each include at least one useful layer ona substrate. The method includes providing an initial structure thatincludes a useful layer having a front face on a support substrate.Atomic species are implanted into the useful layer to a controlled meanimplantation depth to form a zone of weakness within the useful layerthat defines first and second useful layers. Next, a stiffeningsubstrate is bonded to the front face of the initial structure. Thefirst useful layer is then detached from the second useful layer alongthe zone of weakness to obtain a pair of semiconductor structures with afirst structure including the stiffening substrate and the first usefullayer and a second structure including the support substrate and thesecond useful layer.

[0009] Advantageously, the method includes implanting by introducingatomic species through the front face of the useful layer to form thezone of weakness. In addition, the useful layer is provided at asufficient thickness to provide multiple first and second useful layersduring further processing. In a preferred embodiment, the techniqueincludes repeating the implanting, bonding and detaching steps on theuseful layers of the first and second structures to provide a third andfourth semiconductor structures, with the third structure including asecond stiffening substrate and a third useful layer, and the fourthstructure including a third stiffening substrate and a fourth usefullayer. In a variation, the first and second useful layers are providedat sufficient thicknesses to provide multiple third and fourth usefullayers during further processing. Such structures are suitable for usein electronic, optoelectronic or optic applications.

[0010] In an advantageous implementation, included is at least oneintermediate layer in the initial structure between the useful layer andthe support substrate. In another variation, an intermediate layer isprovided in the second structure between the stiffening substrate andthe first useful layer. Such intermediate layers are preferably made ofat least one of silicon dioxide (SiO₂), silicon nitride (Si₃N₄), a highpermitivity insulating material, diamond or strained silicon.

[0011] In another advantageous implementation, bonding is achieved bymolecular adhesion. In addition, at least one of the support substrate,the stiffening substrate, or the useful layer is made of a semiconductormaterial. The support substrate and/or the stiffening substrate mayinclude at least one layer made of at least one of silicon, siliconcarbide, sapphire, diamond, germanium, quartz, yttrium-stabilizedzirconia or an alloy of silicon carbide. In addition, the useful layermay be made of at least one of silicon, silicon carbide, sapphire,diamond, germanium, silicon-germanium, a group III-V compound or a groupII-VI compound, and the support substrate may be made of asingle-crystal or poly-crystal silicon, the useful layer is made of asingle-crystal silicon, and the stiffening substrate is made of asingle-crystal or poly-crystal silicon.

[0012] The methods according to the invention allow at least one pair ofstructures to be formed at the end of each cycle using a single sourcesubstrate which can then be recycled. The present invention is thus moreeconomical to use and commercially feasible than known methods thatrecycle the source substrate. Moreover, as the cycles are repeated, anoperator can choose to use the same or different types of stiffenersubstrates, and can also choose to include one or more intermediate orinterposed layers. The technique according to the invention is thusflexible, allowing for different possible combinations of concomitantlyformed structures that include stacks of different layers.

[0013] Furthermore, depending on the parameters used to implant atomicspecies, it is also possible to create a zone of weakness such that therear or second useful layers are very thin. For example, such thinlayers may be less than 50 nanometers (50 nm) thick, whereas theneighboring front useful layers are much thicker. The thickness of thefront useful layer associated with that of the stiffener which ispressed against it allows for a later thermal annealing treatment thatwill not deform the rear useful layer, and that will not cause blistersto form on the rear useful layer. The result is that a much thinner rearuseful layer can be transferred than presently possible usingconventional methods. Yet further, it has been found that theimplantation of atomic species steps carried out on the substrates ofthe first rank or higher structures concentrate the defects in the frontuseful layers. Consequently, the rear useful layers were not directlysubjected to the implantation, and thus have defects linked to theimplantation and to detachment that extend over a lesser thickness inthe detachment zone than that of the front layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Other aspects, purposes and advantages of the invention willbecome clear after reading the following detailed description withreference to the attached drawings, in which:

[0015]FIGS. 1A to 1C illustrate the different steps of a method ofproducing a structure comprising a useful layer transferred to a supportsubstrate;

[0016]FIGS. 2A to 2C are diagrams illustrating an alternative embodimentof the method represented in FIGS. 1A to 1C according to which astructure is obtained that includes a useful layer transferred to asubstrate via an intermediate layer;

[0017]FIGS. 3A to 3F are diagrams illustrating the different steps of afirst embodiment of the method of concurrently producing at least a pairof structures according to the invention;

[0018]FIGS. 4A to 4F are diagrams illustrating an alternative embodimentaccording to the invention of the method represented in FIGS. 3A to 3F;and

[0019]FIGS. 5A to 5F are diagrams illustrating the different steps of asecond embodiment of the method according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The present method includes forming a first structure 5 or 5′obtained by, for example, using one of the methods whose successivesteps are illustrated in FIGS. 1A to 1C or 2A to 2C. These firststructures are called rank 1 structures. In particular, FIG. 1A shows asource substrate 1 having a zone of weakness 4 that includes two parts:a useful layer 111 and a remainder layer 12 or rear part of the sourcesubstrate. This zone of weakness 4 is the “initial zone of weakness”.

[0021] The source substrate 1 has a “front face” 13 which will come intocontact with a support substrate 2 which will be described later.Advantageously, the source substrate 1 is made of a semiconductormaterial, in particular those commonly used for applications in thefield of electronics, optoelectronics or optics. For example, it couldbe made of silicon, silicon carbide, sapphire, diamond, germanium,silicon-germanium, III-V compounds or II-VI compounds. III-V compoundsare compounds wherein one of the elements appears in column III of theperiodic table and the other appears in column V, such as galliumnitride (GaN), gallium arsenide (AsGa) or indium phosphide (InP). II-VIcompounds are compounds wherein one of the elements appears in column IIof the periodic table and the other appears in column VI, such ascadmium telluride (CdTe). The source substrate 1 can also be a compoundsubstrate, which is a substrate composed of a solid part, for examplesilicon, having an overlying a buffer layer, for example, of silicongermanium (SiGe).

[0022] According to a first alternative embodiment, atomic species couldbe implanted to obtain the initial zone of weakness 4. The phrase“implantation of atomic species” means any bombardment of atomic,molecular or ionic species, which introduces these species into amaterial, with a maximum concentration of the species located at apredetermined depth below the bombarded surface 13. Atomic species canbe implanted in the source substrate 1 by using, for example, an ionbeam implanter or a plasma immersion implanter. Preferably, implantationis carried out by ion bombardment. In addition, the ionic species thatis implanted is hydrogen. Other ionic species can be advantageously usedalone or in combination with hydrogen, such as rare gases (for examplehelium). Other variations of implantation techniques could also be used.

[0023] The implantation results in creating the initial zone of weakness4 in the volume of the source substrate 1 at an average depth ofpenetration of the ions. The zone of weakness 4 extends substantiallyparallel to the plane of the front face 13. The useful layer 11 extendsbetween the front face 13 and this zone of weakness 4.

[0024] This step can be carried out by utilizing the method known underthe registered trademark “Smart Cut”.

[0025] The initial zone of weakness 4 can also be comprised of a porouslayer that is formed, for example, as described U.S. Pat. No. 6,100,166.In this case, the useful layer 11 may be obtained via epitaxy.

[0026] The support substrate 2 acts as a mechanical support and thusgenerally has a thickness of at least about 300 micrometres. It ispreferably made of any single-crystal or poly-crystal semiconductormaterial often used in the aforementioned applications. The supportsubstrate 2 can be a single-layer solid substrate chosen for examplefrom among silicon, silicon carbide, sapphire, diamond, germanium,quartz, yttrium-stabilized zirconia (ZrO₂(YO₃)) and an alloy of siliconcarbide.

[0027] Referring to FIG. 1A, the support substrate 2 has one face 20,termed the “front face” which receives the front face 13 of the sourcesubstrate 1. Then, as represented in FIG. 1B, the front face 13 of theuseful layer 111 is directly bonded onto the support substrate 2 withoutan intermediate layer. Advantageously, this bonding is carried out viamolecular adhesion. After a possible thermal annealing step, theremainder 12 is detached along the initial zone of weakness 4 byapplying stresses (see FIG. 1C). On of the following techniques may beused to detach the remainder: the application of mechanical or electricstresses, chemical etching or the application of energy, for example theuse of a laser, of microwaves, of an inductive heater, or a thermaltreatment in an oven. These detachment techniques are known to thoseskilled in the art and will not be described in any further detail, andcan be used alone or combined. A first rank structure (rank 1) 5 is thusobtained which includes the useful layer 11 transferred to a supportsubstrate 2.

[0028]FIGS. 2A to 2C illustrate an alternative embodiment of the methodwhich has been described with regard to FIGS. 1A to 1C. This alternativetechnique differs in that at least one intermediate layer 3 is insertedbetween the useful layer 11 and the support substrate 2. For reasons ofclarity and simplicity, in FIGS. 2A to 2C and in FIGS. 5A to 5F only oneintermediate layer 3 has been represented, but additional intermediatelayers could be used. Advantageously, each of these intermediate layers3 are made of a material chosen from among silicon dioxide (SiO₂),silicon nitride (Si₃N₄), high permitivity insulating materials, anddiamond. It is also possible to have an intermediate layer made ofstrained silicon on a useful layer of relaxed silicon-germanium (SiGe).In the case where there are several intermediate layers 3, the latterlayer or layers can be either of the same nature or of a differentnature.

[0029] The intermediate layer 3 can be formed via chemical platingtechniques in vapor phase or any other technique known to those skilledin the art. Such techniques could be conducted on either the front face20 of the support substrate 2, on the front face 13 of the sourcesubstrate 1, or on the two front faces. Such a technique is conductedprior to applying or bonding these two substrates against one other.When the intermediate layer 3 is an oxide layer, it can also be formedvia thermal oxidation of one or the other of the two substrates 1 or 2.Irrespective of how the intermediate layers 3 were formed, the freesurface of the upper intermediate layer is bonded to the free surface ofthe substrate 1 or 2 facing it, preferably via molecular adhesion.

[0030] The result of the alternative embodiment of the method is a firstrank structure 5′ that includes the source substrate 2, the useful layer11, and the intermediate layer 3 inserted between them. The word“transferred” herein with regard to a first rank structure signifiesthat a useful layer is transferred to a support substrate via a methodcomprising at least one bonding step, with or without an intermediatelayer 3. According to another embodiment not shown in the figures, theuseful layer 11 can be transferred to the support substrate 2 via theBESOI technique, with or without an intermediate layer 3.

[0031]FIGS. 3A to 3C illustrate a complete cycle of steps of a firstembodiment of the present method, which results in a pair of structureseach comprising a useful layer transferred to a substrate. As shown inFIG. 3A, a zone of weakness 6 is formed on the inside of the usefullayer 11 of the previously obtained first rank structure 5, via theimplantation of atomic species according to the previously describedtechnique for obtaining a zone of weakness. Two layers are thus defined,namely a first or front useful layer 110 and a second or rear usefullayer 120 located between the front useful layer 110 and the supportsubstrate 2.

[0032] As shown in FIG. 3B, a stiffening substrate 71 is adhered to thefree surface 130 of the front useful layer 110, via bonding, preferablyby direct bonding via molecular adhesion. The last step illustrated inFIG. 3C consists of detaching the stacks of layers obtained during theprevious step, along said zone of weakness 6. The layers are detached byapplying stresses according to techniques known to those skilled in theart, and previously described above with regard to FIGS. 1C and 2C.

[0033] Two structures 51 and 52 of a second rank are thus obtained. Thefirst structure 51 comprises the support substrate 2 and the rear usefullayer 120 and the second structure 52 comprises the stiffening substrate71 and the front useful layer 110. It is to be noted that the usefullayer 11 must have a sufficient thickness so that, after detachment, thetwo useful layers 110 and 120 do not have any defects or blisters. Thethickness of the two useful layers 110 and 120 can be identical ordifferent according to the depth of implantation of the atomic speciesand therefore of the localization of the zone of weakness 6. It shouldalso be noted that the useful layer may be of sufficient thickness topermit multiple structures to be formed, which will be explained below.

[0034] It is possible to repeat the cycle of operations that has justbeen described (that is, the creation of a zone of weakness, adhesion ofa stiffening substrate, and detachment along the zone of weakness) withat least one of the structures 51, 52 of the second rank, or to both ofthem. Consequently, one or two pairs of third rank structures 511, 512,521, 522 (see FIG. 3F) are obtained.

[0035] As illustrated in FIG. 3D, the front face 140 of the useful layer110 is subjected to implantation of atomic species to create a zone ofweakness 6, to define a rear useful layer 111 and a front useful layer112. A similar method is used to continue processing with the secondrank structure 51, to obtain a front useful layer 122 and a rear usefullayer 121. The next step is to adhere or bond, via molecular adhesion astiffening substrate 72 to the front face 140 of the front useful layer112 and a stiffening substrate 73 to the front face 150 of the rearuseful layer 122. As shown in FIG. 3F, the next step is to detach thetwo stacks of layers along the zone of weakness 6 so as to obtain fourthird rank structures.

[0036] The two third rank structures 521 and 522 issue from the secondrank structure 52 through use of a stiffener 71 and the rear usefullayer 111 for the first one, and the use of stiffener 72 and the frontuseful layer 122 for the second one. The two third rank structures 511and 512 issue from the second rank structure 51 and include thestiffener 73 and the front useful layer 122 for the first one, and thesupport substrate 2 and the rear useful layer 121 for the second one.

[0037] It is then possible to repeat, if desired, the cycle of the threeoperations that has just been described. The starting structure could beat least one of the rank three structures or of following ranks. Thecycle should end when the useful layers transferred onto a substratereach a thickness above which an extra cycle would result in thetransfer of a poor quality useful layer, meaning one having defects orblisters.

[0038]FIGS. 4A to 4F illustrate an alternative embodiment of the presentmethod. This method is different from that described with reference toFIGS. 3A to 3F in that at least one interposed layer 8 and/or 8″, isinserted between the stiffening substrates 71 and 73, respectively andthe useful layer that faces it. It should be noted that the figures showonly a single interposed layer 8, 8″ for the purposes of simplification,but more such layers could be used.

[0039] The interposed layer 8 or 8″ can be made, for example, viachemical plating in a vapor phase or by any other layer platingtechnique known to those skilled in the art. The interposed layers 8 or8″, respectively, can also be obtained via oxidation of the stiffeningsubstrate 71 or 73, respectively. This plating can be carried out eitheron the stiffener prior to its application onto the useful layer, or ontothe latter, preferably prior to implanting atomic species to create thezone of weakness 6. The interposed layer 8 or 8″ is then bonded to thelayer facing it, preferably by molecular adhesion. For example, theinterposed layers 8, 8″ are made in a chosen material from among silicondioxide (SiO₂), silicon nitride (Si₃N₄), high permittivity insulatingmaterials, and diamond. In the case where there are several interposedlayers 8, 8″, these can be of the same nature or of different natures.

[0040]FIG. 4E shows that the stiffener 72 is directly bonded onto thefront useful layer 112, meaning that it is bonded without an interposedlayer. Four third rank structures are thus obtained, of which only two,reference numbers 521′ and 511′, comprise a stiffener, a useful layerand an interposed layer.

[0041]FIGS. 5A to 5F show a second embodiment of the present method.This method is different from the first embodiment of FIGS. 4A to 4F inthat the starting structure used is the first rank structure 5′,comprising an intermediate layer 3 inserted between the useful layer 11and the support substrate 2. In addition, an interposed layer 8′ is usedbetween the stiffener 72 and the front useful layer 112. This interposedlayer 8′ is of the same nature and is obtained in the same way as thepreviously described interposed layers 8 or 8″.

[0042] Two second rank structures 51′ and 52′, and then four third rankstructures 521′, 522′, 511′ and 512′ are obtained. Each of the thirdrank structures 521′m 52′ and 511′include a stiffener, an interposedlayer 8, 8′ or 8″ and a useful layer. The fourth structure 512′ includesthe support substrate 2, the intermediate layer 3 and the useful layer121.

[0043] The expression “adhere a stiffening substrate onto a usefullayer” herein encompasses the case where there is close contact betweenthe stiffener and the useful layer, and the case where at least oneinterposed layer 8, 8′ or 8″ is present between them. In the differentmethods which have just been described, the expression “stiffeningsubstrate” refers to any type of substrate that acts as a mechanicalsupport and allows for the detachment of the useful layer from thesubstrate from which it issues.

[0044] The choice of the type and/or material (nature) of the stiffener71, 72, 73 depends on the final targeted application for the structure.The stiffening substrates 71, 72, 73 can be chosen from among theexamples given for the support substrate 2.

[0045] The different alternative methods which have just been describedallow at least one pair of structures to be formed at the end of eachcycle for a single source substrate 1 which can then be recycled. Thepresent methods are thus more economical and commercially feasible thanthe known methods which require recycling of the source substrate aftereach structure is created.

[0046] Moreover, upon each cycle repetition, an operator can choose toapply the same type or different stiffeners and can leave out all orinclude at least one of interposed layer 8, 8′ or 8″. The methods arethus flexible, because there is the possibility of concomitantly formingthe structures comprising stacks of different layers.

[0047] Finally, depending on the parameters used to implant atomicspecies, it is also possible to create a zone of weakness 6 so that therear useful layers 120, 111 or 121 are very thin. For example, such thinlayers may be less than 50 nanometers (50 nm) thick, whereas theneighboring front useful layers 110, 112 or 122 may be much thicker. Thethickness of the front useful layer associated with that of thestiffener which is pressed against it allows for a later thermalannealing treatment that will not deform the rear useful layer, and thatwill not cause blisters to form on the rear useful layer. The result isthat a much thinner rear useful layer can be transferred than presentlypossible using conventional methods such as the SMART-CUT® method.

[0048] Additionally, the implantation of atomic species steps carriedout on the substrates of the first rank or higher structures concentratethe defects in the front useful layers 110 or 122. The rear usefullayers 120 or 121 were not directly subjected to the implantation andthus have a zone with defects linked to the implantation and to thedetachment extending over a lesser thickness in the detachment zone thanthat of the front layer.

[0049] The following is a description of an example of the presentmethod with reference to FIGS. 5A to 5F.

EXAMPLE 1

[0050] The first rank structure used here is a SOI substrate typestructure 5′ that includes a support substrate 2 of single-crystalsilicon, an intermediate layer 3 of silicon dioxide SiO₂ having athickness of 20 nm, and a useful layer 11 of single-crystal siliconhaving a thickness of 1.5 μm. A zone of weakness 6 is created byimplanting hydrogen ions based on an implantation energy of about 150keV and an implantation dose of about 6.10¹⁶H⁺/cm². A rear useful layer120 is thus created having a thickness of 20 nm. A single-crystalsilicon stiffener 71 having an interposed layer 8 of silicon dioxideSiO₂ of a thickness of 20 nm is then applied. The two structures arethen detached along the zone of weakness 6 to simultaneously obtain apair of SOI substrates 51′ and 52′. The cycle of the operations is thenrepeated using the second rank SOI substrate 52′ as a startingstructure.

[0051] Once the surfaces have been prepared, the front useful layer 1112has a thickness of about 0.6 microns and the rear useful layer 111 has athickness of about 0.6 microns. When a single-crystal silicon stiffener72 covered in a layer of silicon dioxide 8′ of a thickness of 20 nm (20nanometers) is used, two third rank SOI substrates 521′ and 522′ areobtained after detachment that have respective useful layers 111 and 112that are about 0.6 microns thick.

What is claimed is:
 1. A method for concurrently producing at least apair of semiconductor structures that each include at least one usefullayer on a substrate comprising: providing an initial structure thatincludes a useful layer having a front face on a support substrate;implanting atomic species into the useful layer to a controlled meanimplantation depth to form a zone of weakness within the useful layerthat defines first and second useful layers; bonding a stiffeningsubstrate to the front face of the initial structure; and detaching thefirst useful layer from the second useful layer along the zone ofweakness to obtain a pair of semiconductor structures with a firststructure including the stiffening substrate and the first useful layerand a second structure including the support substrate and the seconduseful layer.
 2. The method of claim 1 wherein the implanting includesintroducing atomic species through the front face of the useful layer toform the zone of weakness.
 3. The method of claim 1 wherein the usefullayer is provided at a sufficient thickness to provide multiple firstand second useful layers during further processing.
 4. The method ofclaim 3 which further comprises repeating the implanting, bonding anddetaching steps on the useful layers of the first and second structuresto provide a third and fourth semiconductor structures, with the thirdstructure including a second stiffening substrate and a third usefullayer, and the fourth structure including a third stiffening substrateand a fourth useful layer.
 5. The method of claim 4 wherein the firstand second useful layers are provided at sufficient thicknesses toprovide multiple third and fourth useful layers during furtherprocessing.
 6. The method of claim 4 wherein the structures are suitablefor use in electronic, optoelectronic or optic applications.
 7. Themethod of claim 1 which further comprises at least one intermediatelayer in the initial structure between the useful layer and the supportsubstrate.
 8. The method of claim 7 wherein the intermediate layer is atleast one of silicon dioxide (SiO₂), silicon nitride (Si₃N₄), a highpermitivity insulating material, diamond or strained silicon.
 9. Themethod of claim 1 which further comprises providing an intermediatelayer in the second structure between the stiffening substrate and thefirst useful layer.
 10. The method of claim 9 wherein the intermediatelayer is at least one of silicon dioxide (SiO₂), silicon nitride(Si₃N₄), a high permitivity insulating material, diamond or strainedsilicon.
 11. The method of claim 1 wherein the bonding is achieved bymolecular adhesion.
 12. The method of claim 1 wherein at least one ofthe support substrate, the stiffening substrate, or the useful layer ismade of a semiconductor material.
 13. The method of claim 1 wherein thesupport substrate includes at least one layer made of at least one ofsilicon, silicon carbide, sapphire, diamond, germanium, quartz,yttrium-stabilized zirconia or an alloy of silicon carbide.
 14. Themethod of claim 1 wherein the stiffening substrate includes at least onelayer made of at least one of silicon, silicon carbide, sapphire,diamond, germanium, quartz, yttrium-stabilized zirconia or an alloy ofsilicon carbide.
 15. The method claim 1 wherein the useful layer is madeof at least one of silicon, silicon carbide, sapphire, diamond,germanium, silicon-germanium, a group III-V compound or a group II-VIcompound.
 16. The method of claim 1 wherein the support substrate ismade of a single-crystal or poly-crystal silicon, the useful layer ismade of a single-crystal silicon, and the stiffening substrate is madeof a single-crystal or poly-crystal silicon.